Presently known automatic transmissions provided on such type of light-weight vehicles are composed of a variable speed drive including a drive pulley and a driven pulley, each pulley consisting of movable flanges on which a transmission belt is mounted; these pulleys have a variable effective diameter responsive to the speed of rotation, the effective diameter increasing with an increase in speed.
In such transmission system, there are several disadvantages. First, an intermediate support is usually provided for the driven pulley resulting in additional space being required on the small vehicle. Also, under certain atmospheric conditions which cause the formation of frost on the pulley flanges and on the transmission belt, the latter will slide over rather than engage the pulleys. Further, a small misalignment on the pulleys inevitably results in a premature wear of the transmission belt and a considerable loss of power.